A coalition of advocates for third parties in presidential elections is filing a lawsuit Monday against barriers to entry in presidential debates.

Alleging that the Federal Election Commission and the Commission on Presidential Debates have fostered a duopoly in American politics that has made it impossible for a third-party candidate to win the White House, the suit seeks to upend a decades-old debate system, while striking a blow against the 150-year Democrat-Republican regime.

Organized by the group Level the Playing Field, which sprung out of the failed 2012 third party effort “Americans Elect” and backed by multi-millionaire financier Peter Ackerman, the lawsuit includes both the Green Party and Libertarian National Committee. It comes as the American public is more dissatisfied with the traditional party system than ever before, and the prospects for fixing it are especially dim.

“It’s the little rules that nobody can see that make all the difference,”…